The assignee of the present invention has pioneered the concept of an aerodynamically released actuator latch for hard disk drives. By way of examples, the reader's attention is directed to commonly assigned U.S. Pat. No. 4,538,193 for "Aerodynamically Released Safety Latch for Data Transducer Assembly in Rotating Rigid Disk Data Storage Device". The disclosure of the referenced patent is incorporated herein by this reference. The reader's attention is further directed to commonly assigned U.S. Pat. No. 4,647,997 for "Aerodynamic Latch for Disk File Actuator"; U.S. Pat. No. 4,692,829 for "Magnetically Biased Aerodynamically Released Integral Safety Latch for Rigid Disk Drive"; and, U.S. patent application Ser. No. 07/839,870 for "Airflow Generator Spindle Hub for Aerodynamically Released Disk Drive Actuator Latch", now abandoned; the disclosures of which are also incorporated herein by reference.
Aerodynamically released shipping latches of the type described in the reference patents have proven very successful in operation. The distinct advantage of an aerodynamically released shipping latch and its manner of operation are explained in these prior patents. Several drawbacks of aerodynamically released shipping latches in accordance with the inventions described in the cited patents have remained unsolved until the present invention. One drawback has been associated with the use of mechanical hair springs which are required in order to provide a sufficient reverse bias force to the latch in order to cause it to engage the rotary data transducer assembly in order to lock the transducer at inner landing zone regions of the data surfaces of the storage disks. Installation of the delicate hair springs during drive assembly has proven to require a difficult manual procedure which has not been well suited to automatic or robotic assembly procedures for high volume production. Also, the reverse bias force applied by mechanical hair springs has tended to be substantially constant, irrespective of the degree of angular deflection caused by air flow from the rotating disks, which has required that the bias force be sufficiently high to overcome any static friction associated with the moving aerodynamic latch member and the base or frame of the device to which such moving member is journalled.
Another drawback of the prior aerodynamic latches has been associated with use over a substantial range of angular displacement. It was heretofore believed that the shipping latch should rotate over a fairly substantial angle in response to air flow in order to be assured that the air flow generated by disk rotation was sufficient to sustain the data transducers in "flying" formation closely above the data surfaces of the disks before they were permitted to depart from their respective landing/parking zones. Also, a substantial degree of rotation of the latch was required in order to permit the latch to be installed after the disk stack has been mounted to the drive spindle during disk drive assembly.
One more drawback has been associated with the use of a separate counterweight which has required additional parts and steps in the latch/drive manufacturing process. Commonly assigned U.S. Pat. No. 4,692,829 describes a safety latch for a storage device, for locking the transducer carriage to restrain the data transducer to a predetermined latching zone during non-rotation of data storage disks and for releasing the carriage in reponse to airflow generated by disk rotation. The latch mechanism includes a moveable airvane disposed between two disks for being deflected by airflow generated by rotations of the disks and latching member responsive to the deflection of the airvanes to release the carriage. In this patent, the latch includes a magnetic spring comprising two outboard magnets for providing a magnetic bias spring for providing a predetermined bias by magnetic field deflection to the latch in order to urge the latch into engagement with the carriage in the absence of airflow sufficient to deflect the airvane to overcome the bias and thereby release the latch. The magnetic spring in this patent included two small plastic magnets 62 and 64 to have north poles on major surfaces facing each other, as shown in FIGS. 1 and 3. The magnet 62 is seated in a shallow recess 66 formed in the latching portion 50 of the member 32, and the magnet 64 is seated in a similar recess 68 formed in the inside of the sidewall 12 of the frame. The magnets 62 and 64 are flat and shallow, and present their oppositely facing, like pole faces in a manner which generates maximum repulsion when the member 32 is maximally deflected due to air flow. The two forces create a state of equilibrium, and in operation, the two magnets 62, 64 do not actually contact each other. The sizes, locations and magnetic field strength characteristics of the magnets 62 and 64 are selected to provide suitable reverse bias force to the member so that it will be positively and reliably urged to engage the notch 54 when airflow from disk rotation diminishes to a point that the reverse bias from the magnets 62, 64 exceeds the airflow force. The above described magnetic bias spring arrangement, although effective in operation, has not proven to be cost effective and has seen diminished practical utility as hard disk drives become smaller. For example, in a 31/2" form factor hard disk drive, this type of magnetic bias spring requires special attention to mounting arrangements and methods for installing the opposed-field permanent magnets, and has obviously required additional components and expenses associated therewith.
A torsion spring has also been utilized on a molded plastic air lock barrel as a bias against the deflection of the latch assembly, see e.g. FIG. 2 of referenced U.S. Pat. No. 4,647,997. These springs can be relatively costly compared to the overall cost of the disk drive. In addition, the torsion spring tends to wander up the airlock barrel and fall off. In this type of arrangement, assembly of the spring, which comprised wrapping the spring around the barrel, was difficult. Finally, vendors are unable to consistently produce torsion springs with the required angular tolerances.
A need has risen for an aerodynamically released shipping latch that does not require the additional bias magnetic spring, mechanical hair spring or torsion spring associated with prior art. The present invention addresses such a need.